Jfi6 Singular Halo of the Moon. 



have hitherto delayed, in order, if poffible, to gain farther information in the neighbourhood 

 concerning it. 



During the fhort continuance of the fmall halo, which did not exceed ten minutes after 

 I got notice of it, I Could not lay my hands on any other inftrument, to take the angles, but. 

 a Siflbn's theodolite, which imlucklily^ having been conftrudied fo as not to admit of a ver- 

 tical angle fo great as the moon's altitude then was, I laid it afide, not recoUefting that it 

 might have meafured feveral of the fmaller angles. But I obferved fundry marks, from 

 which I took the angles as exactly as I could next day. 



The moon was about fouth-weft, and her altitude nearly 54°, which, of confequence, 

 was alfo the higheft altitude of the limb of the greater halo where it was higheil, and 

 where it paffed tlirough the moon ; the altitude of its oppofite limb was 14° ; fo that its 

 diameter fubtended an angle of no lefs than a hundred and-twelve degrees. 



The diameter of the fmall halo, which appeared to be a perfefl; circle, with the moon in its- 

 centre, I found, after repeated trials, was under 12°, and more than 8° ; but as the different 

 diameters of the large halo were not meafured, it cannot pofitively be affirmed, that it was an 

 exa£l circle ; on the contrary, its limb did not feem to interfeft the fmall circle quite fo 

 much at right angles as the circular arch delineated in the plan. It may,, therefore, have 

 been fomewhat elliptical. 



The fmall circle was remarkably bright, particularly at "Weft Refton, about five miles to 

 the northward, the only other place where the halo was obferved, and where it was thought 

 to fend forth flame. The fmall halo alfo continued there much longer than here, where fome 

 thin fleecy clouds foon put an end to it ; but the large halo continued with us near an hour. 



The weather about this time was, for the feafon, remarkably mild, particularly on the 

 day of the halo. The fky was pretty clear all that day, and- alfo in the evening ; but, at 

 the time of the halo, there was a fmall degree of hazinefs, particularly towards the north, 

 which did not, however, prevent the moon from fhining with brightnefs ; and the ftars 

 were even vifible within the circle of the fmall halo : there was little or no wind. 



The circles, or belts, of both halos are reprefented in the plan nearly of their apparent 

 fcreadth, or, perhaps, a little broader : the light of both was whitifh, and confiderably 

 bright, without colour ; that of the large circle was the paler of the two, particularly 

 where it paffed through the fmall circle : to the northward it was fomewhat obfcure. 



By means of tlie angles taken as above, after having afcertained, on a vertical circle of the 

 heavens, the fituations of the moon, of the fmall halo, and of the north-eaflern Kmb of the 

 large halo, whofe fouth-weflern limb pafTed through the moon, the whole was projefted on 

 the horizontal plane, as in. the figure already referred to. The moon, a little more than 

 half, is placed in the centre of the fmaller halo ; and both halos are reprefented in their 

 true fituations, relatively to the horizon, and in the circular fliape which they appeared to 

 have ; though they ought, perhaps, to have been fomewhat forefliortened, and thrown into 

 an elliptic form. 



This halo, as you wdll fee by the above defcription, appears to be of the kind called by the 

 learned a corona ; and as it fomewhat refembles the famous one of the fun obferved at 



Rome 



